Formula One champions Red Bull recognised on Saturday they were well behind rivals in pre-season testing but dismissed reports that Sebastian Vettel had "thrown a hissy fit" about the situation.

Four-times champion Vettel and his team have suffered a string of setbacks due to the new Renault power unit and the problems continued in Bahrain on Saturday with the German breaking down on his first lap of the day.

Vettel helped marshals push the stricken RB10 back to the garage.

Red Bull team principal Christian Horner told Sky Sports that speculation Vettel had thrown a tantrum when he first tested the car back in January was "complete and utter rubbish".

"I don't know where that came from about Sebastian," he added. "He is fine, he understands that there are issues and he is trying to help the team where he can.

"There has not been one raised voice, one bit of discontent. He has just got his head down and he has a huge amount of trust in the team."

The Red Bull website also carried a highly sarcastic report from their "F1 Spy" about the rumour mill.

Vettel, it joked, had sent the team a postcard to say sorry and decided to spend a couple of weeks chilling out watching daytime soaps and eating crisps round at former team mate Mark Webber's house.

While Red Bull and some of the other Renault-engined teams have been struggling to string a significant number of laps together, Mercedes and Ferrari-powered rivals have been doing race simulations.

Vettel's new Australian team mate Daniel Ricciardo, preparing for a home season-opener in Melbourne on March 16, said on Thursday the team was still "not up to scratch" with time running out.

Ricciardo had a more positive day on Friday but Saturday brought more gloom and Horner said the team was "still definitely on the back foot.

"This is the 10th day of testing and we are about 10 days behind I reckon," he added.

Horner said cooling issues that had sidelined the team during the first team in Jerez, Spain, had been addressed and Red Bull were working hard with Renault to fix other problems that had emerged.

"We still have another two weeks before Melbourne, for sure we will be bringing more parts to Melbourne. It would just be great if we could have another couple of days like we had yesterday."